1. Field of the Invention
The present invention relates to a mobile phone, and more particularly to a technique which suppresses power consumption in a waiting operation of a mobile phone.
2. Description of the Related Art
Conventionally, a mobile phone has been come into a practical use. In the mobile phone, a waiting operation peculiar to the mobile phone is carried out in addition to a usual operation such as speech communication and data communication. A substantial function of the mobile phone is not realized during the waiting operation. Therefore, a control is carried out during the waiting operation to prevent power consumption of a battery.
A control unit used in a conventional mobile phone will be described with reference to FIG. 1. The conventional control unit is composed of a central processing unit (CPU) 10, a main clock generator 11, a wait clock generator 12, a wait timer 13 and a main counter 14.
The main clock generator 11 generates a main clock signal to operate the control unit and supplies to the CPU 10 and the main counter 14. The CPU 10 operates in response to the main clock signal to control the whole control unit of the mobile phone. The main counter 14 carries out a counting operation in response to the main clock. The CPU 10 controls communication between a base station and the mobile phone in accordance with the count value of the main counter 14.
The wait clock generator 12 generates a wait clock signal and supplies to the wait timer 13. The wait timer 13 operates in response to the wait clock. The wait timer 13 generates a start signal and supplies to the main clock generator 11. Also, the wait timer 13 generates an interruption signal and supplies to the CPU 10. Thus, the wait timer 13 controls an operation before and after a waiting operation.
In the above configuration, the operation of the control unit of the conventional mobile phone will be described. The CPU 10 specifies a wait time before entering the waiting operation, and then issues a main clock stop instruction to the main clock generator 11. Also, the CPU 10 issues a wait timer start instruction to the wait timer 13. By this, the main clock generator 11 stops the generation of the main clock signal. As a result, the CPU 10 enters a sleep mode and the counting operation of the main counter 14 is stopped.
When the specified wait time elapses in the sleep mode, the wait timer 13 supplies a start signal to the main clock generator 11 to restarts the main clock generator 11 and supplies an interruption signal to the CPU 10 to restart the operation of the CPU 10. Thus, the counting operation of the main counter 14 is restarted and the CPU 10 can communicate with a base station in accordance with the count value of the main counter 14. The power consumption of a battery can be suppressed because the main clock signal is stopped in the waiting operation through above operation. However, the count value of the main counter becomes discrete before and after the waiting operation.
By the way, in the frequency division multiple access (FDMA) and the time division multiple access (TDMA) which are adopted in the conventional mobile phone, because the status of the CPU can be generally changed from the waiting operation in accordance with the reception of electric wave from the base station, there is not a problem, even if the count value of the main counter become discrete.
Also, in the mobile phone of the code division multiple access (CDMA) system, continuity of the count value of the main counter before and after the waiting operation is required. However, the main clock signal is low in frequency and is near the frequency of the wait clock signal. For this reason, it is possible to correct the count value of the main counter by searching for a few clocks to maintain the continuity of the count value of the main counter.
However, in the wide band—code division multiple access (W-CDMA), because the frequency of a main clock signal is high considerably, compared with the frequency of the wait clock. For this reason, it is impossible to correct the count value of the main counter to maintain the continuity of the count value before and after the waiting operation. Moreover, in the W-CDMA system, it is not possible to carry out communication if the count value of the main counter is shifted by one clock. Therefore, in the W-CDMA system, it is necessary that the main clock signal is not stopped even during the wait operation or the communication synchronization with the base station is established again after the wait operation.
If it is supposed that the main clock signal is not stopped during the wait operation, the power consumption during the wait operation becomes larger tens of times, compared with the case where the main clock signal is stopped. Also, if it is supposed that the communication synchronization is established again after the wait operation, a process time after the wait operation becomes 10 times or more, resulting in increase of the power consumption.